The present invention generally relates to soft-durometer compounds of polyvinyl chloride (PVC) and nitrile rubber (NBR). More particularly, this invention relates to PVC/NBR compounds useful in sealing members, mounts, tubing and contact members in floor cleaning units.
The seals, mounts, tubing and contact members that are common in many of the presently available floor cleaning units are generally formed from thermoplastic vulcanizate compounds. Although the requisite physical and chemical properties of these elements are different for each specific application, it will be appreciated that these elements are made from compounds of low to medium range durometer inasmuch as it is necessary that such elements be flexible and compressible, with compression set being particularly important for the seals, mounts and contact members, and flexibility being particularly important for tubing (wherein the durometer of the rubber compound may be higher, i.e., harder, than that for seals, mounts and contact members).
While these various elements are currently formed from materials having acceptable chemical and physical properties, there is always a drive for cost savings in the production of any end product, and the present invention focuses upon providing elements for floor cleaning units at an appreciable cost savings. Under current technology, the elements of concern are generally formed of thermoplastic compounds that are processed with appropriate fillers, lubricants, and other processing aids to provide the desired physical and chemical properties. However, in many cases, the thermoplastics employed and/or the processes for formulating the desired thermoplastic compounds are costly.
Polyvinyl chloride is widely available and is generally less expensive than the materials commonly compounded to create the seals, mounts, tubing and contact members of many floor cleaning units. However, PVC has a poor compression set and poor flexibility, and therefore, without some alteration, PVC is not suitable for the fabrication of such elements. The present invention employs PVC-based compounds modified with nitrile rubber for the provision of seals, mounts, tubing and contact members in floor cleaning units, without sacrificing, and, at times, improving upon the physical and/or chemical properties of the end product element.
In general, the present invention provides floor cleaning units that include at least one PVC/NBR component selected from the group consisting of seals, mounts, tubing, and contact members. The PVC/NBR component includes a polyvinyl chloride base resin and, based upon 100 parts by weight of said polyvinyl chloride base resin:
(a) from about 10 to about 50 parts nitrile rubber, as an impact modifier;
(b) from about 30 to about 100 parts plasticizer; and
(c) from about 1 to about 4 parts polyvinyl chloride stabilizer.
In a particular contact member embodiment, the present invention provides a floor cleaning unit that includes a contact member including a polyvinyl chloride base resin and, based upon 100 parts by weight of said polyvinyl chloride base resin:
(a) from about 20 to about 40 phr nitrile rubber,
(b) from about 60 to about 100 phr plasticizer,
(c) from about 1 to about 5 phr polyvinyl chloride stabilizer,
(d) from about 10 to about 15 phr epoxide plasticizer,
(e) from about 0.05 to about 0.4 phr internal lubricant, and
(f) from about 0.7 to about 1.5 phr external lubricant.
In a particular sealing member embodiment, the present invention provides a floor cleaning unit that includes a sealing member including a polyvinyl chloride base resin and, based upon 100 parts by weight of said polyvinyl chloride base resin:
(a) from about 20 to about 40 a phr of nitrile rubber,
(b) from about 60 to about 100 phr of plasticizer,
(c) from about 1 to bout 5 phr of polyvinyl chloride stabilizer, and
(d) from about 10 to about 15 phr of epoxide plasticizer.
To facilitate molding of these sealing members, the following ingredients may also be added:
(e) from about 0.05 to about 0.4 phr internal lubricant, and
(f) from about 0.7 to about 1.5 phr external lubricant.
In another embodiment, a foamed sealing member is provided. A floor cleaning unit includes a foamed sealing member including a polyvinyl chloride base resin and, based upon 100 parts by weight of said polyvinyl chloride base resin:
(a) from about 20 to about 40 phr of nitrite rubber,
(b) from about 75 to about 125 phr of plasticizer,
(c) from about 1 to about 5 phr of polyvinyl chloride stabilizer,
(d) from about 10 to about 15 phr of epoxide plasticizer, and
(e) from about 0.5 to about 1.5 phr of blowing agent.
In yet another embodiment, tubing is provided. A floor cleaning unit includes tubing including a polyvinyl chloride base resin and, based upon 100 parts by weight of said polyvinyl chloride base resin:
(a) from about 20 to about 40 phr of NBR;
(b) from about 50 to about 80 phr of plasticizer;
(c) from about 1 to about 5 phr of PVC stabilizer;
(d) from about 3 to about 8 phr of epoxide plasticizer;
(e) from about 5 to about 15 phr filler;
(f) from about 0.05 to about 0.4 phr internal lubricant; and
(g) from about 0.5 to about 1.2 phr external lubricant.
A process for producing soft durometer polyvinyl chloride compounds such as those provided above is also provided. The process includes the sequential steps of adding PVC resin to a mixer and heating, under agitation, to a temperature of from about 140xc2x0 F. to about 170xc2x0 F.; adding plasticizer and stabilizer to the PVC resin and raising the temperature to from about 185xc2x0 F. to about 195xc2x0 F.; adding at least one ingredient selected from fillers, blowing agents, pigments, internal lubricants and external lubricants and raising the temperature to from about 220xc2x0 F. to about 240xc2x0 F.; transferring the resultant mixture to a cooling mixer and lowering the temperature to the range of from about 120xc2x0 F. to about 70xc2x0 F.; adding nitrite rubber to the cooled mixture; and feeding the resultant nitrile rubber mixture to an extruder to shear and fuse the mixture at a temperature of from about 280xc2x0 F. to about 350xc2x0 F. The nitrite rubber mixture may be formed into pellets at the extruder, and the pellets may subsequently be formed into any of the useful parts for floor cleaning units.